The present invention relates to a sample holder for electron microscope and more particularly, to an apparatus which can make possible electrical measurement of a desired inward position of a sample inside a transmission electron microscope and a scanning transmission electron microscope as well and at the same time, can enable electron microscopic observation of the portion undergoing electrical measurement to be achieved.
With fine machining dimension and high integration of a semiconductor device, a magnetic device and the like advanced, deterioration in device characteristics and degradation in reliability have become problematic more seriously than before. In recent years, for the sake of analyzing faults in an nanometer area in a semiconductor device to ascertain an essential cause of a fault in the course of development and mass production of a new process, such expedients as spectroscopic analysis and two-dimensional element distribution analysis have become indispensable which use (scanning) transmission electron microscopy ((STEM), electron energy loss spectroscopy (EELS) and energy dispersive X-ray spectroscopy (EDX).
Conventionally, in evaluating characteristics of the device, a probe for measurement of electrical characteristics is brought into contact with terminal portions disposed on the device, a portion determined faulty as a result of electrical measurement is extracted with a focused ion beam unit and thereafter, high resolution observation and element analysis of the faulty portion are carried out by means of a (scanning) transmission electron microscope and a concomitant analysis units, thereby ascertaining causes of faults.
In the above method, however, a portion first determined faulty is observed subsequently with an electron microscope and so electron microscopic observation cannot be conducted concurrently with measurement of electrical characteristics. To cope with this problem, an on-the-spot observation technique has been disclosed in, for example, JPA-2005-091199 (Patent Document 1), JP-A-2007-273489 (Patent Document 2), JP-A-2006-331979 (Patent Document 3) and JP-A-2003-035682 (Patent Document 4), according to which the electron microscopic observation is carried out while applying a voltage inside an electron microscope.
Patent Document 1 discloses an internal structure observation apparatus in which a probe provided inside an electron microscope is brought into contact with a sample located in the electron microscope by means of a probe movement control unit, a voltage is applied to an arbitrary portion of the sample and then, a change in internal structure of the sample caused by the voltage application is detected with a detector.
Patent Document 2 discloses a technique, according to which, in a sample holder for transmission electron microscope, a probe base mounted with a plurality of probes is provided, a sample for observation can be located on the sample holder body, a piezoelectric device is disposed which makes movable at least either the probe base or the sample and a probe is brought into contact with the sample to permit a voltage to be applied to an arbitrary inward portion of the sample.
Patent Document 3 discloses a sample holder for electron microscope, with which measurement points are selected from an observed image and measurement of electric resistance between at least two nearby points can be conducted. The sample holder is provided with at least two probes for current measurement which are adjustable in position in three axial directions inclusive of a direction of insertion of the sample holder and besides, a probe position precise adjustment mechanism is provided which can bring these probes into contact with desired inward positions of the sample.
Patent Document 4 discloses a technique, according to which in a process of machining an arbitrary region of an objective sample into minute sample pieces by using a charged particle beam and picking up sample pieces, a fine electric conductor is attached to a picked-up sample piece and a voltage is applied to the attached fine electric conductor.
According to the techniques disclosed in the Patent Documents, by applying voltage to a sample inside the electron microscope, internal electrical characteristics of the sample can be measured and besides electron microscopic observation of a location where the voltage is applied can be achieved.
In the internal structure observation apparatus disclosed in Patent Document 1, a probe is brought into contact with an inward portion of a sample provided inside the electron microscope and voltage is applied to the inward portion of the sample by way of the contacted probe. The probe is associated with a probe movement control unit for moving the probe, so that the probe can be moved to a desired position, contacted to the inward portion of the sample and electrical characteristics can be measured.
But, in the electron microscope, the sample location position is in a narrow space defined by magnetic pole pieces of an objective lens and in addition, a detector such as for EDX is also provided, with the result that the region around the sample is limited and it is difficult to move the probe freely from the periphery of the electron microscope to bring it into contact with the observation sample of the electron microscope.
Disclosed in Patent Documents 2, 3 and 4 is the technique according to which in a limited inner space of the electron microscope, a probe is provided inside the sample holder and the probe is brought into contact with an observation sample of the electron microscope.
In the case of Patent Document 2, however, at least two probes are disposed and the piezoelectric device for driving the probes is provided but the probes are all disposed on the probe base which is driven by the piezoelectric device, so that all probes are moved at a time. This makes it difficult to bring the probe into contact with a desired inward position of the sample.
In the case of Patent Document 3, with the view of moving at least two probes independently in three axial directions inclusive of the entry direction of the sample holder, linear movement mechanisms (micrometer heads) and piezoelectric devices are provided in individual axial directions of the individual probes.
But, when two probes are used, six linear movement mechanisms in total are necessary in the system of Patent Document 3 and consequently, the sample holder increases in weight on the side opposite to the side where the sample is located, thus increasing the influence of sample drift, for instance. Further, the piezoelectric device is remote from the probe for contact to the sample and therefore, when the piezoelectric devices are used for bringing the probe into contact with the sample, individual differences of the piezoelectric devices need to be taken sufficiently into consideration.
Further, in the case of the sample holder of Patent Document 3, the interior of the sample holder is placed in vacuum condition and so an O ring is interposed between the outer cylinder of the holder and a support member for the linear movement mechanism. Accordingly, the region to be maintained in vacuum is widened and in the electron microscope used in high vacuum, time for pumping to vacuum is caused to be prolonged in the event of deterioration of the vacuum degree inside the electron microscope proper or upon mount/dismount of a sample.
In Patent Document 4, a desired sample in a device is extracted with a focused ion beam unit and an electric conductor is fixed to part of the sample by using beam assist deposition. Thereafter, the sample is admitted to the inside of the electron microscope, with the result that electrical characteristics of the portion fixedly mounted with the electric conductor can be measured and the electron microscopic observation can be achieved but electrical characteristics identification and electron microscopic observation cannot be achieved at portions other than the portion fixedly mounted with the electric conductor.